Method and device for generating an error signal in a motor vehicle

ABSTRACT

A method and a device for generating an error signal in a motor vehicle. In this context, the vehicle has a drive engine as well as an actuating arrangement which can be actuated by the driver of the vehicle, and with the assistance of which a braking system is activated. Further, a detecting arrangement detects an actuation of the actuation arrangement. A wheel drag torque quantity is determined which represents the drag torque caused by the engine at the vehicle wheels. Moreover, a deceleration quantity is determined which represents the longitudinal deceleration of the vehicle. Furthermore, a braking quantity is determined which represents the operating state of the actuating arrangement. The error signal is then generated as a function of the determined drag torque quantity, the determined deceleration quantity, and the determined braking quantity. Thus, it is possible to perform diagnostics on the safety-relevant brake lights switch without requiring additional outlay for hardware.

BACKGROUND INVENTION

The present invention relate to method and a device for generating anerror signal in a motor vehicle respectively.

In modern vehicles, the brake lamps are generally controlled as afunction of a brake pedal actuation. To this end, a brake lights switchis activated by the brake pedal operated by the driver. The position ofthis switch signals a brake actuation, and, apart from the brake lightcontrol, can also be utilized, for example, for controlling the engineand/or the transmission. A defect in such a brake lights switch must bedetected as quickly and as reliably as possible, since a defective brakelights switch can signify that different vehicle functions are not beingproperly executed.

SUMMARY OF THE INVENTION

An object of the present invention is to generate an error signal in asimple manner which will indicate a defect in such a brake lightsswitch.

As mentioned before, the present invention starts out from a method anda device for generating an error signal in a motor vehicle. In thiscontext, the vehicle has a drive engine, as well as an actuatingarrangement for activating a braking system. Further, a detectingarrangement are provided for recognizing an actuation of the actuatingarrangement. According to the present invention a wheel drag torquequantity is determined which represents the drag torque produced by theengine at the vehicle wheels. Moreover, a deceleration quantity isascertained which represents the vehicle's longitudinal deceleration.Also determined is a braking quantity which represents the operatingstate of the actuating arrangement. The error signal is then generatedas a function of the determined drag torque quantity, the determineddeceleration quantity, and of the determined braking quantity.

Thus, according to the present invention the monitoring of the brakelights switch is carried out on the basis of the interpretation of thelongitudinal dynamics determined, for example, from the wheel speeds,the wheel drag torque determined, for example, with the assistance ofthe engine drag torque and the gear transmission ratio. The presentinvention enables diagnostics to be performed on the brake lightsswitch, which is relevant to safety, without requiring additional outlayfor hardware.

In this context, as mentioned, the actuating arrangement can be designedas a brake pedal, and the detecting arrangement as a brake lights switchthat is used to detect a brake pedal actuation.

It is particularly advantageous for the error signal to represent theproper or the improper condition of the detecting arrangement, and,furthermore, for an indicating arrangement to be provided which altertheir operating state in response to the generated error signal.

One advantageous embodiment of the present invention provides fordetermining an engine drag torque quantity that represents the enginedrag torque, and a gear transmission ratio quantity that represents thegear transmission ratio currently adjusted between the vehicle engineand the driven vehicle wheels. The wheel drag torque quantity is thendetermined as a function of the ascertained engine drag torque quantityand the ascertained gear transmission ratio quantity.

One particularly advantageous embodiment of the present inventionprovides for the error signal to represent the proper or the impropercondition of the detecting arrangement, and for the determineddeceleration quantity to be compared to a first predefinable thresholdvalue, and for the determined wheel drag torque quantity to be comparedto a second predefinable threshold value. The error signal is thengenerated long the lines of an improper condition if

the determined deceleration quantity exceeds the first threshold value;and

the determined wheel drag torque quantity falls below the secondthreshold value; and

the determined braking quantity represents that operating state of theactuating arrangement in which no actuation of the actuating arrangementis detected.

To determine the deceleration quantity, preferably the wheel speeds ofthe vehicle wheels and/or the vehicle's longitudinal deceleration aredetected.

To generate the error signal, it is also possible to consider a signalthat represents the operating state of a clutch arranged in the powertrain of the vehicle. In particular, the error signal should only begenerated when the clutch is closed.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a block diagram according to the present invention.

FIG. 2 shows a flow chart representing a process according to thepresent invention.

DETAILED DESCRIPTION

In FIG. 1, reference symbol 11 denotes a vehicle engine whose functionsare controlled by engine control unit 11 a in open or closed loop. Theengine torque currently existing at the output end of engine 11, inparticular engine drag torque M_(s,mot), is present in engine controlunit 11 a, and is fed to control unit 15.

Engine 11 is connected to the drive wheels of vehicle 14 via a clutchand/or a torque converter 12 via transmission 13. The functions of thetransmission are controlled by transmission control unit 13 a in open orclosed loop. Present in transmission control unit 13 a is generally thecurrently adjusted gear transmission ratio i, which is fed to controlunit 15.

Longitudinal acceleration a_(l) of the vehicle is detected by sensor 14a and fed to the control unit.

The actuation of brake pedal 16, which can be actuated by the driver ofthe vehicle, is detected by brake lights switch 16 a. The position(BS_(on) or BS_(off)) of brake lights switch 16 a is fed to control unit15. Generally, the position (BS_(on/off)) of brake lights switch 16 a,as a standard, is read in by modern engine control units. Control unit15 generates error signal F, which is used to trigger an error light 17,as a function of the input signals. This will be explained in greaterdetail on the basis of FIG. 2.

In this context, the division shown in FIG. 1 between engine controlunit 11 a, transmission control unit 13 a, and control unit 15 isselected merely for the sake of better clarity. However, functions ofthe mentioned individual control units can be executed in each of theother control units, as well. Thus, for example, control unit 15 andengine control unit 11 a, in particular, can be combined into one unit.The gear transmission ratio can also be determined in the engine controlunit or in the combined control unit, respectively, for example, withthe assistance of a simple evaluation of the engine and transmissionoutput speeds. The longitudinal acceleration can be determined, forexample, on the basis of the transmission output speed or the wheelspeeds, respectively, in a differentiating.

Subsequent to the starting step 201 shown in FIG. 2, the mentioned inputsignals, position BS_(on/off), the vehicle's instantaneous longitudinalacceleration a_(l), instantaneous engine drag torque M_(s, mot), as wellas the currently adjusted gear transmission ratio i are read in in astep 202. In step 203, wheel drag torque M_(s,rad) acting at the drivewheels is generated from engine drag torque M_(s,mot) and the geartransmission ratio.

The following can lead to a vehicle deceleration:

1. An ascending roadway (uphill) grade can lead to a vehicledeceleration due to overcome the difference in altitude.

2. Shifting, in particular shifting down, can lead to a vehicledeceleration.

3. If the driver of the vehicle uses the accelerator to reduce theengine torque, this can result in a longitudinal vehicle deceleration

4. A brake actuation leads to a vehicle deceleration.

According to the present invention, the position of brake lights switch16 a (BS_(on/off)) is compared to specific quantities for diagnosticpurposes. In this context, one has to exclude the above mentioned cases1 through 3, where a vehicle deceleration is not caused by a brakeactuation.

One can distinguish between cases 1 through 4 through a comparison 204of the engine or wheel acceleration al, respectively, with a thresholdvalue SW1. In all probability, a substantial vehicle deceleration (queryresult “Y” in step 204) can only be caused by a braking intervention.

Cases 2 and 3 can be detected through a comparison 205 of theinstantaneous wheel drag torque M_(s,rad) with a threshold value SW2. Ifwheel drag torque M_(s,rad) suffices (query result “Y” in step 205),then, in accordance with the present invention, error signal F shouldnot be generated for safety reasons. However, if the vehicle'slongitudinal deceleration is great enough, and the wheel drag torqueM_(s,rad) is low enough, then a brake actuation is present, and brakelights switch 16 a emits signal BS_(on). This is checked in step 206. Ifthis is the case, one goes over directly to final step 208. However, ifthis is not the case, then brake lights switch 16 a is defective, whichis indicated by generation of error signal F via indicating arrangement17.

Subsequent to final step 208, the sequence shown in FIG. 2 is startedagain.

What is claimed is:
 1. A method for generating an error signal in amotor vehicle including a vehicle engine for driving the vehicle, anactuating arrangement capable of being actuated by a driver of thevehicle and for activating a braking system, and a detecting arrangementfor detecting an actuation of the actuating arrangement, the methodcomprising the steps of: determining a wheel drag torque quantityrepresenting a drag torque caused by the engine at wheels of thevehicle; determining a deceleration quantity representing a longitudinaldeceleration of the vehicle; determining a braking quantity representingan operating state of the actuating arrangement; and generating theerror signal as a function of the determined wheel drag torque quantity,the determined deceleration quantity, and the determined brakingquantity.
 2. The method according to claim 1, wherein: the actuatingarrangement corresponds to a brake pedal, and the detecting arrangementcorresponds to a brake lights switch.
 3. The method according to claim1, further comprising the step of: providing an indicating arrangementfor changing an operating state in response to the generated errorsignal, wherein: the error signal represents one of a proper conditionand an improper condition of the detecting arrangement.
 4. The methodaccording to claim 1, further comprising the steps of: determining anengine drag torque quantity representing an engine drag torque;determining a gear transmission ratio quantity representing a geartransmission ratio currently adjusted between the engine and the wheelsof the vehicle that are driven; and determining the wheel drag torquequantity as a function of the determined engine drag torque quantity andthe determined gear transmission ratio quantity.
 5. The method accordingto claim 1, further comprising the steps of: comparing the determineddeceleration quantity with a first predefinable threshold value;comparing the determined wheel drag torque quantity with a secondpredefinable threshold value; and generating the error signal if: thedetermined deceleration quantity exceeds the first threshold value, thedetermined wheel drag torque quantity falls below the second thresholdvalue, and the determined braking quantity represents the operatingstate of the actuating arrangement in which no actuation of theactuating arrangement is detected, wherein the error signal representsone of a proper condition and an improper condition of the detectingarrangement.
 6. The method according to claim 1, further comprising thestep of: detecting at least one of wheel speeds of the wheels of thevehicle and a longitudinal acceleration of the vehicle in order todetermine the deceleration quantity.
 7. The method according to claim 1,further comprising the step of: considering a signal representing anoperating state of a clutch arranged in a power train of the vehicle inorder to generate the error signal.
 8. A device for generating an errorsignal in a motor vehicle including a vehicle engine for driving thevehicle, an actuating arrangement capable of being actuated by a driverof the vehicle and for activating a braking system, and a detectingarrangement for detecting an actuation of the actuating arrangement,comprising: an arrangement for determining a wheel drag torque quantityrepresenting a drag torque caused by the engine at wheels of thevehicle; an arrangement for determining a deceleration quantityrepresenting a longitudinal deceleration of the vehicle; an arrangementfor determining a braking quantity representing an operating state ofthe actuating arrangement; and an arrangement for generating the errorsignal as a function of the determined wheel drag torque quantity, thedetermined deceleration quantity, and the determined braking quantity.9. The device according to claim 8, further comprising: an enginecontrol unit for controlling the engine according to one of an open loopand a closed loop as a function of data present in the control unit.